Backup generator glossary

Automatic transfer switch (ATS) — the device that senses an outage, disconnects your house from the grid, starts the generator and transfers the load, then reverses when utility power returns. Installation labor is around $1,200. Manual transfer switch — same isolation function, but you throw it by hand.

Running watts — the continuous power an appliance draws. Starting watts (surge) — the much larger brief draw a motor needs to spin up; central air can need roughly three times its running wattage. Sizing formula: total running watts plus the highest single starting wattage.

Backfeeding — electricity flowing from a generator back through your service into utility lines. It endangers utility workers and is the reason Ready.gov and every utility warn against plugging a generator into a wall outlet. Exercise cycle — the automatic weekly self-test a standby unit runs for several minutes to keep the battery charged.

SAIDI / SAIFI — EIA's reliability measures: SAIDI is the minutes per year the average customer is without power (662.6 in 2024 including major events), SAIFI is the number of interruptions (1.531 in 2024). Inverter generator — a portable that conditions its output for cleaner power, safer for electronics. kW — kilowatt; 1 kW is 1,000 watts, so a 22 kW generator is rated at 22,000 watts.

How to choose

Learn 'transfer switch' first

It's the safety-critical component and the line item most often shuffled between quotes.

Never let anyone blur running and starting watts

A quote sized on running watts alone will trip out the first time the AC or well pump starts.

Recognize 'backfeed' as a stop word

Any proposal that involves energizing house wiring without a transfer switch ends the conversation.

Ask what the exercise cycle schedule is set to

You want to know the day and time so silence becomes a signal.

Convert kW to watts when comparing to your load list

Your appliance list is in watts; the generator spec is in kilowatts. Multiply by 1,000 before you compare.